A sufficiently sensitive method which will permit early, localized, noninvasive detection of atherosclerosis does not currently exist. Atherosclerosis will be accelerated in Beagle dogs by the technique of I131 thyroid ablation and a high cholesterol diet. Ultrasound pulsed Doppler and ultrasound echo-track techniques which require no surgical penetration of the skin will be used chronically to measure changes in cardiovascular hemodynamics, vessel geometry, and mechanical response of the vessel wall caused by increasing atherosclerotic plaque deposition. Changes in 1) the intraluminal blood velocity profile and flow rate, 2) the circumferential Young's modulus of the arterial wall, 3) the distribution of viscous shear stress at the wall will be correlated with atherosclerotic plaque formation at known foci in large arteries of dogs. Groups of animals will be sacrificed after specific atherogenic diet durations, and the arteries will be fixed at the mean arterial pressure. Microscopic examination of transverse sections taken at small intervals along the segments previously studied transcutaneously will provide gross measures of the magnitude of the plaques. Histology will be performed to determine the type and composition of the plaques. Comparasions will be made between hemodynamic changes in arteries affected by plaque deposition and controlled flow disturbances in tube models. The ultrasound data will be recorded on magnetic tape and analyzed off line using analog to digital conversion facilities and the CDC 6400 digital computer. The recorded data will be averaged, the variance calculated, velocity profiles at different instants of the cardiac cycle plotted and the time varying flow plotted. The role of viscous shear stress and other hemodynamic parameters in the localization of atherosclerotic plaque deposition will be investigated. The proposed research will provide the background for the development of techniques for noninvasive detection of atherosclerosis in man.